Nitrogen removal is one of the most difficult problems facing municipalities and sewer authorities throughout the world. A number of factors contribute to the problem. While there has been significant advancement in nitrogen removal through biological treatment, still from a technical point of view, it is very complicated to effectively and efficiently remove nitrogen utilizing any approach or process. This is especially true in view of the very low nitrogen limits now being promulgated by many governmental bodies. Moreover, efficient nitrogen removal requires a wastewater treatment facility having a relatively large capacity and that in turn requires substantial capital expenditures. Many authorities charged with treating wastewater have limited budgets and consequently are severely restricted in terms of their ability to build adequate treatment facilities that will accommodate efficient and effective nitrogen removal processes.
In the past, many of the more successful nitrogen removal processes have been designed to be utilized in relatively large wastewater treatment facilities. Invariably, many of these large wastewater treatment facilities are not designed with a great deal of flexibility. That is, certain basins are designated nitrification basins while other basins are designated denitrification basins. Consequently, it is difficult to vary nitrification and denitrification capacities within that facility. Thus, depending on conditions, there is little opportunity to vary the nitrification and denitrification capacity of the facility to achieve optimum results relative to ammonia and nitrogen removal.
Other types of nitrification and denitrification processes have been designed for use in alternating treatment systems. See for example, U.S. Pat. No. 5,137,636 assigned to I.Kruger Systems A/S of Denmark. Here, the ratio of nitrification time to denitrification time can be adjusted and can be controlled to where the denitrification time constitutes more than fifty (50%) percent of the total operation time of the process. Although this process has met with success, it is appreciated from a review of the disclosure of U.S. Pat. No. 5,137,636, that the process calls for the flow of wastewater through all three basins. In addition, the third basin is continuously maintained under aerobic conditions and does not contribute to denitrification, which under many conditions could be an advantage. Further, the third tank is normally of a different construction, has a smaller volume and different process eqipment than the other two, which is less desirable from a construction as well as an operational point of view.
There has therefore been and continues to be a need for a nitrification and denitrification process that is relatively simple to control, cost efficient, which has maximum flexibility in altering and adjusting that ratio of nitrification time to denitrification time and at the same time can meet very strict effluent demands with respect to nitrogen.